Quantifying the bathymetric stripping gravity corrections of global seawater and major lakes over Turkey

Authors: MEHMET SİMAV, HASAN YILDIZ

Abstract: Gravity data inversion or interpretation requires the removal of the gravitational effects of the a priori known geologic and/or morphologic features within the Earth?s system to model and reveal the remaining signals of the unknown anomalous subsurface density distributions. The Bouguer gravity anomalies reduced by the normal gravitational field of the Earth and the gravitational attraction of the topographic masses above the sea level are frequently used in geophysics for this purpose. However, density contrast effects of the other major known elements, such as offshore seawater, inland water bodies, glaciers, and/or sediments can be removed from the Bouguer gravity anomalies, which is denoted as stripping in gravimetry, to unmask the remaining gravitational signal of the sought anomalous masses. Stripping the Bouguer anomaly off seawater density contrast has become possible with the releases of freely available high-resolution global ocean bathymetry data. Moreover, the bathymetry data from recent hydrographic surveys over the inland water bodies with high-precision echo sounders has given rise to the opportunity to determine the stripping effects of the lake water density contrast. In this study, we quantify the global seawater bathymetry stripping effects along with lake water stripping of some greatest Turkish lakes on a regular 1' × 1' grid at the Earth's surface over Turkey including offshore. The seawater bathymetric corrections vary from 132 to 418 mGal over the seas and show a long-wavelength pattern over the inland with a mean value of 133 mGal. It produces significant variations onshore close to the coasts and on some islands up to 163 mGal. Although the bathymetric gravity stripping due to the lake water density contrast has negligible effects on their surrounding land areas, the water masses can produce notable effects on the lake surfaces reaching up to few tens of mGals at their deepest area, which should be considered in the microgravimetry studies over the lakes.

Keywords: Global seawater bathymetric stripping, lake water bathymetric stripping, gravity anomaly, forward modelling, Turkey

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